How to say someone out of office in short time on phone call?

I usually pick a phone that addresses to my collogues who is not in the office for 5 or 10 mins. They probably go to the other departments and will come back soon. I usually tell that "He is out of the office and will be back soon". The callers sometimes misunderstood. So, they ask me "Is he on annual leave?".

Could someone please tell me what is the best way to say in that situation?

Thanks

Solution 1:

Try "He stepped out of the office."

step out, [no object] to leave a place, esp. for a short time:

Ms. Jones has just stepped out of the office for a moment.

http://www.wordreference.com/definition/step%20out

(Cross-posted with @qweradsf.)

Solution 2:

"I'm sorry, but he's just stepped out for a few minutes. Can I take a message?"